Level control valves of this type have an adjustment drive which scans the height of the vehicle structure above the vehicle axle and relays a correction value to the level control valve in order to be able to keep a constant vehicle height despite different loading of the vehicle structure. The adjustment drive is often constructed as swivelable actuation lever, the swivel movement of which is converted to a translational movement of the valve tappet which, with a double valve body, forms an outlet valve. An inlet valve is formed between the double valve body and an edge constructed as seat. The inlet and outlet valves serve for admitting air to and discharging air from the air suspension bellows. An arbitrary raising and lowering is not possible with level control valves of this type; in contrast, the control is inevitably effected in dependence on the adjustment drive.
A level control valve of the type described at the beginning is known from German Patent 3,716,436. This level control valve has the customary inlet and outlet valve, via which the admission of air to and discharge of air from the connected air suspension bellows are effected with small strokes of the valve tappet. With large strokes, the longitudinal throttle changes its cross-section and a largely unthrottled admission of air to and discharge of air from the downstream air suspension bellows are effected. Insofar as a plurality of air suspension bellows are connected to a level control valve, a transverse throttle function is also fulfilled, via which, insofar as air bellows are connected on different sides of the vehicle, any rolling deflections occurring when the vehicle turns are kept within limits. In order to allow an even more rapid discharge of air from the air suspension bellows if, for example in container operation, a relatively large load is lifted from the vehicle in a short time, or even in the unloading of goods to be dumped, it is known to arrange a second outlet valve on the level control valve. However, this second outlet valve cannot be actuated arbitrarily either, but in dependence on the adjustment drive of the level control valve. For arbitrary raising and lowering, the level control valve is interconnected with an alternating-load valve within a system in a single or multiple arrangement, it being possible for the alternating-load valve to be controlled electrically. However, the system becomes complicated by the use of an alternating-load valve and one or more level control valves. Additionally, appropriate line connections must be provided between the valves.
German Patent 3,445,579 also shows a control system for the arbitrary raising and lowering of the vehicle structure of vehicles with air suspension, in which control system an alternating-load valve in the form of a pilot valve and corresponding level control valves are likewise used. The pilot valve indeed allows the actuation of the positions stop, raise, lower and drive and thus fulfills all the necessary functions. However, in this case too, the outlay is substantial.
There are various operating states of commercial vehicles with air suspension, in which the customary functions of a level control valve must be fulfilled, for example a defined longitudinal and transverse throttle characteristic with small strokes in comparison to large strokes, and, for example, an adjustability of the close-off position. However, it is not always necessary for air to be able to be admitted to and discharged from the air suspension bellows arbitrarily rapidly in the sense of the use of an alternating-load valve. Thus it is sufficient, for example for commercial vehicles to be transported in ferry operation, to provide an arbitrary lowering possibility for the vehicle structure while the admission of air can also be effected more slowly via the normal inlet valve of the level control valve. With semi-trailers and trailers it is sometimes desirable to carry out the loading and unloading operation of goods in the lowered position of the vehicle structure. With truck trailers it can be desirable to lower the towing vehicle for rapid removal of the semitrailer. Even the rapid lowering of the semitrailer itself may be sensible in some situations.
Setting out from these situations, the problem arises of providing a level control valve having longitudinal and, if appropriate, transverse throttle characteristics, with which level control valve it is possible to lower the structure or vehicle frame of a commercial vehicle arbitrarily and rapidly without the use of an additional alternating-load valve.
According to the invention, this is achieved in that the level control valve has a shutoff and outlet valve which acts independently of the adjustment drive and is of large cross-section for the rapid lowering of the vehicle structure, and in that, for each line leading to an air suspension bellows, a bypass line is provided which leads from said line to the shutoff and outlet valve of large cross-section, in which bypass line there is arranged in each case a non-return valve which opens in the direction of the shutoff and outlet valve. Thus a shutoff and outlet valve of large cross-section is arranged integrated in the level control valve, specifically a shutoff and outlet valve of the type which acts independently of the adjustment drive, that is to say can be arbitrarily actuated or controlled. The details of the shutoff and outlet valve can be constructed in a variety of ways, for example as directly actuatable valve within the level control valve or, with the advantages of remote control, as servo controlled valve. Important factors are, on the one hand, the construction of large cross-section for the rapid venting and, on the other hand, a shutoff function in respect of an advanced part of the storage line against simultaneous venting of the storage line and well.
Despite integration of a shutoff and outlet valve of large cross-section in the level control valve, the constructional outlay for this level control valve is only slightly greater. The shutoff and outlet valve can be arbitrarily controlled independently of the position of the adjustment drive, i.e. the position of the adjustment drive has no effect on the shutoff and outlet valve. Of course, in a servo-controlled shutoff and outlet valve it is necessary in some way to feed the corresponding control pulse to the shutoff and outlet valve of the level control valve. In particular in the sense of a remote control, this is necessary and sensible if the level control valve, as often happens, is installed approximately in the longitudinal mid-axis of a vehicle below the vehicle structure. The bypass line or the bypass lines bypass the normal inlet and outlet valve on the level control valve. They connect the port or the line which leads to the air suspension bellows to the storage line to the level control valve. Thus likewise large cross-sections can and should be implemented in the bypass lines in order to allow the rapid venting via the shutoff and outlet valve. As a result of the arrangement of the non-return valve(s), the transverse throttle function possibly implemented at the level control valve during normal driving continues to be effective. The rapid lowering possibility of the vehicle structure does not otherwise act in a disturbing manner on the longitudinal throttle characteristic, that is to say for the throttled admission and discharge of air with small strokes and for the unthrottled admission and discharge of air with large strokes.
The new level control valve is considerably less complicated in comparison to the use of one or more level control valves in conjunction with an alternating-load valve. For many applications, a rapid lowering of the vehicle structure is sufficient; it is not absolutely necessary also to allow a rapid raising again. The positioning of the normal structure height in relation to the axles can readily be effected via the inlet valve which is present in any case.
It is particularly advantageous if the shutoff and outlet valve of large cross-section is constructed as rapid-release valve and consequently has a valve body which closes off the seat of the associated outlet valve under prestress, acts under pressure from the storage line as overflow valve to the inlet valve and, when the storage pressure is removed, shuts off the overflow valve under pressure in the opposite direction and opens the associated outlet valve. In this case, in this servo-controlled construction of the shutoff and outlet valve, a diaphragm or a piston-type closure piece is provided which is expediently guided with an overflow sleeve in a bore hole in the housing of the level control valve and which cooperates with the associated outlet seat, from which a venting channel feeds either directly to the atmosphere or to the atmosphere via the outlet orifice provided in any case at the level control valve. A rapid-release valve of this type provides considerably large cross-sections for the venting.
The new level control valve can be interconnected within a system having a pilot valve which is arranged in the storage line which is advanced to the level control valve. The pilot valve can be electrically or manually actuatable and has its own venting arrangement. It is understood that a plurality of level control valves can also be arranged downstream from a pilot valve of this type. However, it is also possible to arrange a solenoid valve on the housing of the level control valve and connected in the storage line, it being possible for the shutoff and outlet valve to be controlled independently of the adjustment drive via the electrical actuation of said solenoid valve. An electrical actuation of this type requires little outlay and allows the level control valve also to be readily arranged in the longitudinal axis of the vehicle below the vehicle structure. It is also possible in a simple manner to implement a height restriction on the level control valve via the arrangement of a solenoid valve. This merely additionally requires a sensor which is activated when a certain height of the structure above the vehicle axles is exceeded and it passes a signal to the solenoid valve in the sense of a rapid lowering of the vehicle structure.
The shutoff and outlet valve can have its own vent orifice on the housing of the level control valve, which vent orifice is then likewise designed to have a correspondingly large cross-section. However, it is also possible to provide a corresponding connection channel in the housing of the level control valve, which connection channel leads from the shutoff and outlet valve to the outlet orifice of the level control valve which is normally already provided.
The shutoff and outlet valve can be inserted in the storage line leading to the inlet valve. Its shutoff function is then particularly important in the sense of preventing the simultaneous venting of the storage line as well.
A plurality of ports can also be provided, each having a line leading to an air suspension bellows and each having a bypass line leading to the shutoff and outlet valve of large cross-section, each having a non-return valve. Despite this multiple arrangement, the transverse throttle characteristic is not eliminated.
The bypass line can branch off in the region of the port for the line leading to the air suspension bellows and have a larger cross-section than the bore hole leading to the inlet valve and to the outlet valve. This also serves for maintaining the transverse throttle function.
The solenoid valve can be constructed and switched in such a way that it produces the connection in the storage line in the currentless state. Thus it is ensured that, in the case of a power failure, the vehicle structure always remains at the normal vehicle height or is returned to this normal position. However, application possibilities are also conceivable, in which the inverse switching could be advantageous.